This invention relates to a heater, especially a heater for vehicles, having a mixture enrichment unit, an ignition device and a burner having a nozzle and a vorticization element, said burner also having a combustion chamber formed by a combustion pipe, from where the burned gases are directed to an exhaust-gas outlet in the heat exchange relationship with a heating medium.
Heaters of the above-mentioned type, which are also called fuel-operated heaters, are generally known. Heaters of this type can be further characterized concerning the provided type of burner, such as a low-pressure burner, a rotational atomizing burner and a high-pressure burner, where a nozzle and a vorticization element are provided.
On the basis of German Pat. No. 30 10 078 and corresponding U.S. Pat. No. 4,395,225, a liquid-fuel-operated burner for heating devices is known having a low-pressure atomizer. In order to achieve an automatic temperature-dependent control of the total amount of primary air traveling through the burner in an especially simple, space-saving and reliable manner, a toroidal chamber is provided in the feeding pipe for the primary supplementary air and in said toroidal chamber, a bimetallic ring is provided forming an air valve and controlling the air passage as a function of the temperature.
On the basis of German Auslegeschrift No. 25 52 265 and corresponding British Pat. No. 1,556,733, a rotational atomizing burner is known, for example, that is designed in such a way that an arrangement of charges is achieved that produces a relatively rich mixture only in the area of the ignition zone, i.e. the area of the plug, in order to ensure a secure ignition of said mixture. In the burning chamber, a thin walled and largely self-supporting lining plate is provided that surrounds the rotor at a distance, is penetrated by the ignition plug and is heated very rapidly by the ignition flame of the outlet side of the burner due to a circumferential entrainment of the fuel, so that it acts as an evaporator and contributes very significantly to an enrichment and an increase of the ignitability of fuel-air mixture where it is lean.
From German Offenlenungsschift No. 18 03 815, an arrangement on a combustion chamber for avoiding coking is known, where in the area of the mixture-enrichment zone or of the burning space, a heat pipe is arranged that is preferably formed as an annular cylinder. This heat pipe constitutes a heat-conducting and heat-compensating device. Such a heat pipe is formed by a hollow metallic part containing a material having a capillary effect, such as a copper fiber, and a small amount of liquid. When the heat pipe is heated, the liquid evaporates and, by means of the capillary effect, distributes the heat evenly over the whole surface of the heat pipe, so that the temperature gradient is negligibly small. By means of this heat pipe, the combustion chamber, over its whole length, is kept at an evenly high temperature in order to avoid coking and to achieve a blue burning of the preferably liquid fuel.
German Pat. No. 975 176 discloses a heating device for motor vehicles, especially motor vehicles with an underfloor or rear engine, where the combustion chamber, by means of a constricting ring, is subdivided into a combustion chamber and a post-combustion chamber.
In the case of all these known heaters, achieving optimized combustions still remains a problem, especially in view of the CO.sub.2 and CO values of the exhaust gases and the smoke spot number; said problem being all the more urgent, the more exhaust-gas emission values of such units are restricted by governmental regulations to increasingly lower values and the CO.sub.2 -value in this case corresponds largely to the stoichiometric combustion. If these exhaust gas emission values are to be reduced, this has only been possible by accepting a less favorable burning efficiency of the heater. Another difficulty, in the case of the previously known heaters, is the noise emission, where a need exists to obtain a noise emission that is as low as possible.
The invention, therefore, has a primary object of developing a heater of the above-mentioned type in such a way that, a noise emission that is as low as possible can be obtained, yet an extremely favorable efficiency of the heater and of the combustion can be achieved, along with optimization of the combustion values, especially the CO.sub.2 -values, the CO-values and the smoke spot number.
According to a preferred embodiment of the invention, a heater is developed for this purpose, and especially a heater for vehicles, through the use of an insert for supporting the flame within the combustion pipe that forms an annular space arranged concentrically along the combustion pipe and projecting into the combustion chamber.
More particularly, the insert supporting the flame in the combustion pipe for the combustion chamber should be as thin and short as possible, so that it has a very small mass of its own. This insert has the effect that it has a very small mass of its own. This insert has the effect that the flame and the heat generated by it is concentrated in a space that is as small as possible. Consequently, the combustion mixture evaporation is increased, especially in this area or space, so that very favorable burning conditions and a significantly more complete combustion than previously was obtained is achieved. In fact, for example, the CO.sub.2 -value of the burned gas can be increased to about 15%, which ensures a better efficiency during combustion.
When the insert has only a small mass of its own, it can be heated to operating temperature very rapidly, and it also cools off very rapidly after the heater is turned off. As a result, when the heater is turned on, a very short smoke phase is achieved so that the heater according to the invention, also, has a low smoke spot number at ignition and no further soot is produced during operation.
In a surprising manner, the insert according to the invention, which is formed in an uncomplicated manner, can result in a significant improvement in the case of heaters of the mentioned type, with respect to the efficiency as well as to the exhaust-gas emission values.
Favorable results may, especially, be achieved when the length of the insert, in the longitudinal direction of the combustion pipe is selected in such a way that it is approximately equal to the diameter of the insert. In the case of these dimensions, it is not only ensured that the length of the insert is dimensioned to be as short as possible, but also that the space formed by the insert, where the flame is concentrated, has optimal dimensions in regard to achieving complete combustion.
For a further improvement of the concentration of the flame in the space formed by the insert, the insert in the area of its downstream, open, end has a narrowing of its diameter. The ratio of the diameter of the narrowing to the diameter of the insert is preferably about 1:1.25.
Preferably, the annular space between the insert and the combustion pipe is filled with a heat insulating material so that the insert, by means of the insulation, is thermally insulated from exhaust gases flowing along the exterior of the combustion pipe to the exhaust-gas outlet, especially in the proximity of the burner, in order to avoid a heating of the exhaust gases in this area. This results in a lowering of the exhaust gas temperature by up to 25.degree. C., and improves the efficiency with respect to fuel-engineering of such a heater even further.
In the case of a high-pressure burner having a nozzle and a vorticizing element, there is the additional advantage that the insert supporting the flame makes it possible that the nozzle tolerances may have a more extensive dispersion range and may therefore have a greater dispersion in the spraying pattern.
The measures according to the invention also permit a reduction of the noise emission of such a heater, and a more quietly operable heater is especially advantageous in regard to motor vehicle heaters when the passenger area is to have as little noise as possible.
In the case of certain burners intended for household purposes, for example, where the heat transfer to the heating medium takes place in a manner that is different than in the case of the described embodiment, the combustion pipe may be detached from the insert, so that only the insert is provided.
These and further objects, feature and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiments in accordance with the present invention.